The present invention relates to retrograde cannulas, and in particular to retrograde cannulas used in the delivery of cardioplegia and having automatically expandable sealing members.
Retrograde cannulas are commonly employed during certain cardiac surgical procedures, in order to deliver cardioplegia into coronary veins to effect cardiac arrest by depolarizing cell membranes.
In order to occlude the coronary sinus, the distal end of the cannula includes a sealing member such as an expandible balloon adapted to seal against a wall of the coronary sinus. Balloons may be of the manual-inflating or auto-inflating type. In the auto-inflating type (also referred to as self-inflating), the balloon is in fluid communication with the CPG being delivered to the blood stream and is inflated thereby.
In manual-inflating cannulas, fluid for inflating the balloon is added or withdrawn by means of a syringe. When the balloon of a manual-inflating cannula is deflated, it is common for the balloon to retract snugly against the cannula body when not inflated, whereby the cannula has a reduced profile to facilitate insertion and removal into the body.
In contrast, auto-inflate retrograde catheters typically include a balloon having a relatively permanent shape which varies little between the inflated and deflated states. The inflation of the balloon mainly serves to make the balloon more rigid or turgid, i.e., more less pliant. Thus, the profile of the cannula is not appreciably reduced when the balloon is deflated. This can lead to problems when attempting to insert the cannula into a patient's vessel.
It has previously been proposed in U.S. Pat. No. 5,197,952 to stretch a cannula prior to insertion thereof into a patient. That involves the fixing of a plug within the infusion lumen in the area of the balloon. The plug forms a barrier against which a stylet can be pushed in order to stretch the cannula. The balloon is provided with a fluid inlet disposed proximally of the plug and a fluid outlet disposed distally of the plug, in order to enable fluid (e.g., CPG) to flow through the balloon (and around the plug) after the cannula has been installed. It will be appreciated that the need to install a plug complicates the manufacture and use of the cannula.
It would be desirable to provide an auto-inflate cannula with the ability to significantly reduce its profile and thereby facilitate insertion and removal of the cannula. It would be advantageous to accomplish this without the need to provide a barrier within the cannula body and/or without having to provide an appreciable restriction to the flow of infusion liquid.